1. Field of the Invention
The present invention relates to an adsorbent for gas, and a gas separation and purification method using the same.
2. Related Background Art
Examples of gas separation and purification methods include methods which employ a chemical reaction against an impurity gas. U.S. Pat. No. 5,783,162 proposes feeding hydrogen into a mixed gas containing oxygen to convert the oxygen into water for removal.
On the other hand, various porous materials have been employed in the past as adsorbents for gas. These porous materials are classified into microporous materials with a pore size of 2 nm or less, mesoporous materials with a pore size of from 2 to 50 nm, or macroporous materials with a pore size of 50 nm or more, and are used according to the size of the adsorbed gas molecule. Furthermore, methods that use an adsorbent which selectively adsorbs an impurity gas for impurity gas separation are often employed. Known methods include, for example, PSA (Pressure Swing Adsorption) which utilizes the difference in the adsorption of argon; and PTSA (Pressure and Temperature Swing Adsorption) which utilizes the difference in the adsorption of argon depending on pressure and the difference in the adsorption depending on temperature. U.S. Pat. No. 6,478,854 proposes a method for separating nitrogen from air using zeolite as an adsorbent which specifically adsorbs nitrogen. Japanese Patent Application Laid-Open No. 2004-074025 proposes an adsorbent obtained by coating a conventional adsorbent with an adsorbent whose adsorption/desorption properties exhibit hysteresis.
In a gas separation method which uses a conventional adsorbent, it is necessary to select an adsorbent which selectively and abundantly adsorbs only the desired gas, and which does not adsorb other constituents. If constituents other than the desired gas are adsorbed, the adsorption pressure of the constituent gas which is to be separated needs to be sufficiently separated from the adsorption pressure of the other constituent gases.